Computer Memory (Slightly on DASD and SASD)

Computer Memory (Slightly on DASD and SASD)

I. DEFINITIONS

Memory is part of the computer that serves as a repository of information that must be set and maintained as well as possible. Memory is usually referred to as: computer storage, computer memory or memory, is a computer device that is used as data storage and information when using the computer. Memory is an essential part of the modern computer and its location in the CPU (Central Processing Unit).

Most computers have a memory hierarchy consisting of three levels, namely:

• physical register in the CPU, being at the highest level. Information that was in the register can be accessed in one CPU clock cycle.
• Primary Memory (executable memory), is in the middle level. For example, RAM. Primary Memory is measured by one byte at a time, can be accessed relatively quickly, and is volatile (information can be lost when the computer is turned off). The CPU accesses memory with a single load and store instructions in a clock cycle.
• Secondary Memory, located in the lower level. For example, disk or tape. Secondary Memory is measured as a collection of bytes (block of bytes), access time is slow, and is non-volatile (the information is retained when the computer is turned off). Memory is implemented in the storage device, so access includes action by the driver and device.

More sophisticated computer has more levels in the memory hierarchy system, ie cache memory and other forms of secondary memory such as rotating magnetic memory, optical memory, and sequntially access memory. However, each level is simply a refinement one of the three basic levels which have been described previously.

Part of the operating system that regulates memory hierarchy called a memory manager. In this era of multiprogramming, the memory manager is used to prevent the process of writing and reading by other processes that are located in the primary memory, manage swapping between main memory and disk when main memory is too small to hold all the processes.

The goal of management is to:

Increase the utility of CPU
Data and instructions can be accessed quickly by the CPU
Efficiency in the use of the limited memory
Transfer from / to main memory to / from the CPU can more efficiently

II. Memory Usage

The main components in a computer system is the Arithmetic Logic Unit (ALU), Control Circuitry, Storage Space and devices Input / Output. If no memory, it only serves as a digital computer signal processing devices, such as calculators or media player. The ability of memory to store data, instructions and information are what make a computer can be called as a general-purpose computer.

Computers are digital devices, the information presented by the binary number system. Text, numbers, images, audio and video is converted into a set of binary numbers (binary digit or bit abbreviated). A set of binary numbers known as BYTE, where 1 byte = 8 bits. The larger the size of its memory so the more information that can be stored in a computer (storage devices). Here are some pictures that can represent how information is stored in memory and how data is transferred from one section to another.

As an example for a binary search of the letter B. So if we press the B button, then the letter B was converted into a binary number 01,000,010. computer so the information received is transferred from one part to another part, for example, from the RAM to the Arithmetic Logic unit, via bus or electronic pathways that exist in the motherboard.

III. MEMORY TYPE (STORAGE MEDIA)

Memory is on computer data storage media, which in computer data storage media is divided into 2 types:

A. INTERNAL MEMORY

This type of memory can be accessed directly by the processor. The internal memory has a function as a reminder. In this case that is stored in the main memory can be either data or program. In more detail, the functions of the main memory is:
Store data from input devices until the data is sent to the ALU (Arithmetic and Logic Unit) for processing

Saving the results of ALU processing before being sent to the output device
Accommodate the program / instruction derived from input device or from a secondary reminder device

Distinguished ordinary memory is divided into two kinds: ROM and Ram. In addition, there are also memory called cache memory.

a. ROM

ROM (Read-Only-Memory aka firmware) is a type of memory that does not lose its contents when it does not have electricity, and at first it can only be read. ROM on a computer provided by the computer vendor and contains the program or data.

On the PC, the ROM called the BIOS (Basic Input / Output System) or ROM-BIOS. Instructions in this BIOS to be run by the microprocessor when the computer is turned on. Generally the process is contained in the BIOS in order are as follows:

• Check the contents of CMOS.
• CMOS (Compmentary Meta-Oxyde Semiconductor) is a type of chip that requires electrical power from the battery. This chip contains a 64-byte memory whose contents can be replaced. This is the variety of settings in the CMOS base computers do, such as appliances used to load the operating system and including the date and time of the system.
• Load handling interrupts (interrupt handlers) and device drivers (device drivers).
• Interrupt handling is a small program that became a translator between the hardware and the operating system. For example, if the user presses a keyboard key is then sent through a gesture keyboard interrupt handling.
• Device drivers is a program that acts as an identity provider for specific hardware (eg scanners) that can be recognized by the operating system.
• Initialize registers and power management
• Testing hardware (POST or the power-on self-test) to ensure that all hardware is in good condition
• Display settings on the system
• Determine which device will be used to run programs (ex.: hard disk)
• Taking the contents of the boot sector. Boot sector is also a small program. By the BIOS program is loaded into RAM and then the microprocessor will execute the command-ering that are already in the RAM.

Through the above procedure is, then the operating system (windows, linux, solaris, etc.) loaded.

In addition to ROM, there is also a chip called a PROM, EPROM and EEPROM.

• PROM (Progammable Read-Only-Memory)
• If the content is determined by the vendor ROM, PROM sold empty and can then be filled with a program by the user. Once filled with the program, the contents of PROM can not be removed.
• EPROM (Erasable Programmable Read-Only-Memory)
• Unlike the PROM, EPROM contents can be removed once programmed. Removal is done by using ultraviolet light.
• EEPROM (Electrically Erasable Programmable Read-Only0Memory)
• EEPROM can store data permanently, but its contents can still be erased electrically through the program. One type of EEPROM is Flash Memory. Flash memory is used in digital cameras, video game consoles, and the BIOS chip.

b. RAM

RAM (Random-Access Memory) is a type of memory whose contents can be changed as long as the computer is turned on and is volatile. In addition, the RAM has properties that can store and retrieve data very quickly.

Various types of RAM on a PC; such as DRAM, SDRAM, SRAM, RDRAM, and EDO RAM.

• DRAM (Dynamic RAM) is a type of RAM that must be periodically refreshed by the CPU so that the data contained in them is not lost.
• EDO RAM (Extended Data Out RAM) is a type of memory used in the system using the Pentium. Suitable for having bus with speeds up to 66 MHz.
• SDRAM (Sychronous Dynamic RAM) is a type of RAM that is a continuation of DRAM, but has been synchronized by the system clock and has a higher speed than DRAM. Suitable for the system bus with speeds up to 100 MHz.
• SRAM (Static RAM) is a type of memory that does not need a refresher by the CPU so that the data contained therein remain stored properly. This type of RAM has a higher speed than DRAM.
• RDRAM (Rambus Dynamic RAM) is a type of memory that is faster and more expensive than SDRAM. This memory is used on systems that use the Pentium 4.
• Types of RAM that are on the market:
• SIMM (single in-line memory module) - Having a capacity of 30 or 72 pins. 30 pin SIMM memory to PC uses 80286 to 80486 times and operate at 16 bits. Memory 72 pin widely used for PCs using Pentium and operates on 32-bit. Speed ​​cited following the term ns (nano second) as 80ns, 70ns, 60ns and so on. The smaller the value the higher speeds. DRAM (dynamic RAM) and EDO RAM (Extended Data Out RAM) using SIMM. DRAM stores bits in a storage cell (storage sell) as an electrical values ​​(electrical charge) to be in-refesh hundred times every moment to set (retain) data. EDO RAM is kind of faster DRAM, EDO takes the output of the data, which he takes in between the CPU and RAM. This type of memory is no longer used on the computer lately. ex: SIMM 30 PIN SIMM 72 PIN.
• DIMM (dual in-line memory module) - Capacity 168 pin, both memory module is active, every surface is 84 pin. SIMM is different than just working on the next module only. Support the 64 bits of data delivery. SDRAM (synchronous DRAM) using DIMM. Is a substitute of DRAM, FPM (fast page memory) and EDO. SDRAM controller (synchronizes) the same memory with the CPU clock so for faster data transfers. There are two speeds are 100MHz (PC100) and 133MHz (PC133). 168 PIN DIMM.
• DDR SDRAM (double-data-rate SDRAM) - The characteristics similar to SDRAM DDR SDRAM, but the transfer of data (data transfer) approaches the speed of the system clock (system clock) and in theory increase the speed of SDRAM. Formerly used as a memory for a separate card but at this point the computer manufacturer makes the memory module to the motherboard as an alternative way to substitute the SDRAM has 184 pins and three kecpatan contained in the 266MHz, 333MHz and 400MHz. 184PIN DIMM.
• DRDRAM (Direct Rambus DRAM) - It used to be recognized as RDRAM. Is a type of SDRAM that is made by Rambus. DRDRAM used for CPUs from Intel high speed. The transfer of data is the same as DDR SDRAM but has two data channels to improve. PC800 is also recognized as having the rate of 400MHz. Operates in the form of 16 bits instead of 64 bits. There currently are DRDRAM speed 1066MHz known as RIMM (Rambus inline memory module). DRDRAM Model 4200 32-bit RIMM deliver 4.2GB at any time at a speed of 1066MHz.

c. CACHE MEMORY

Limited memory capacity, high speed memory and is more expensive than the main memory. Located between the main memory and the processor registers, serves to processors not directly refer to the main memory but in cache memory access speed is higher, the method uses the cache memory to improve system performance.

Cache memory is the fastest type of RAM, and is used by the CPU, hard drive, and a few other components. As with RAM, more cache memory is better, but usually cache on the CPU and hard drive can be upgraded into more. Examples can be seen for example is the Pentium II CPUs are 512 kilobyte cache, and the IBM 9LZX SCSI hard drives are 4 megabytes cache.

As with RAM, in general the data will be passed first in the cache memory before heading components to be used (eg CPU). In addition it also temporarily cache memory stores the data for quick access. Speed ​​cache memory is also an important element. For example, Pentium II CPUs have the cache of 12 k, and has a Celeron CPU at 128 k cache, but the cache on a Pentium II running at 1/2 times the speed of the CPU, while the cache on the Celeron running at the same speed with the speed of the CPU. This is a tradeoff that makes the speed of the Celeron certain things sometimes can even beat the Pentium II.

B. EXTERNAL MEMORY

An additional memory function to store data or programs. Example: Hard drive, Floppy Disk etc.. Relationship between Chace Memory, Main Memory and External Memory can be seen in the following figure.

The basic concept of external memory are:

• Storing data is fixed (non-volatile), either at the time the computer is on or not.
• External memory is also called the external memory hardware to perform a write operation, readout and data storage, outside of main memory.
• External memory has two main purposes, namely as a permanent storage to RAM and the help function to get a cheap high-capacity memory for long-term use.

VARIOUS TYPES OF MEMORY EXTERNAL

1. By Type of Data Access

Based on the type of external memory access is classified into two types, namely:

a. DASD (Direct Access Storage Device) where it has direct access to the data.

Example:

• Magnetic (floppy disk, hard disk).
• Removable hard disk (Zip disk, flash disk).
• Optical Disk.

b. SASD (Sequential Access Storage Device): Access data indirectly (sequential), such as magnetic tape.

2. Based on the Characteristics of Materials
Based on the characteristics of the materials of manufacture, the external memory is classified into several groups as follows:
a. Punched Card or perforated
A small card contains holes that describe various instructions or data. This card is read through the punch card reader that is not used anymore since 1979.

b. Magnetic Disk
Magnetic Disk is a disk made of materials that are magnetic, example: floppy and hard drive.

c. Optical Disk
Optical disks are made of optical materials, such as resin (polycarbonate) and coated with highly reflective surfaces such as aluminum. Example: CD and DVD.

d. Magnetic Tape
While magnetic tape, made of materials that are magnetic but the ribbon-shaped, like a tape recorder.