Cache Memory,  Cache saver UMI,  Computer Memory

RAM Memory

Random Access Memory Random access memory or RAM is volatile memory. Random-access memory is fast memory that loads programs and data being processed. RAM memory is a type of memory that remains active as long as the computer is turned on, when the computer is turned off, all the data are written in the random access memory vanishes and disappears.

RAM loads the programs and data being processed. It is the working memory of the computer, it is the memory that supplies the processor with information.

GARTNER GROUP and META GROUP analysts say the amount of RAM is more important than the speed of the processor. RAM access time is measured in “nanoseconds”, while hard drive access time is measured in “milliseconds”.

Conventional, Paged and Extended Memory

When DOS was first developed, the processors in IBM PC XT and compatible computers could only address a maximum of 1024KB or 1MB of memory. A computer that can only address 1024KB means that it can only locate 1,024,000 different memory locations, or that it can only know 1,024,000 different addresses. Each address corresponds to a datum, and to access this datum, the computer needs to know its address, ie the exact location in the memory where this information is stored.

The maximum addressing capacity of IBM PCs is equal to 1MB, but only a part can be used by DOS applications, and this part of the 1MB is called ” conventional memory “.  “. The other parts were reserved for different use.

Conventional memory corresponds to the first 640 KB (minus a small part at the beginning which is reserved for BIOS data).

In order to overcome the limits of conventional memory (640 KB), several companies, MICROSOFT, INTEL, and LOTUS, have joined forces to define ”  paged memory “. The paged memory makes it possible to go beyond the addressable 640 KB and thus makes it possible to increase the memory used by DOS applications. It becomes possible to increase the RAM memory installed on a computer and to go beyond 1 MB. The expanded memory is also called “LIM specification”, “EMS memory” or “EMS window”. To use the paged memory, it is necessary that the application DOS is compatible, and it is necessary to install a ”  paged memory manager  ” (the EMS manager is a file which is called EMM.SYS or EMM.DRV, and which must be loaded into RAM using a DEVICE command in the CONFIG.SYS system file). The expanded memory manager swaps data between conventional memory and expanded memory.

Technology has evolved and computers with the 80286, 80386, and 80486 microprocessors can “physically” address more than 1MB. AT computers can address up to 16MB, and 386 and 486 computers can address up to 4GB. Memory greater than the first 1MB is called “  extended memory  ”. To use extended memory, you also need to install an ”  extended memory manager  “; and DOS applications that use it must be compatible.

Above 1MB, memory modules or memory cards that are added to the motherboard must be identified by the motherboard as additional memory (whether it is expanded or extended memory). Jumpers on the motherboard allow this identification. Sometimes, for AT computers , you also need to define all of the memory (conventional, paged, and / or extended memory) in the CMOS component ROM. Memory modules or memory cards also have jumpers or switches that allow you to set the type of memory, paged or extended, and allow you to set their ”  base address  ” (that is, at what level in all memory).

Dynamic or static

RAM memory RAM can be dynamic or static:

Dynamic RAM ( DRAM ) stores electrical charges (which correspond to a bit equal to one) for a short period of time, and data that needs ‘be kept for a longer period, receive a new electric charge, they are said to be “refreshed”.

Static RAM ( SRAM ) maintains the electric charge.

Virtual memory simulates an expansion of the RAM on the hard disk

If the RAM is insufficient, thena swap file is created on the hard disk to simulate an extension of the random access memory, this is the virtual memory .

The speed of accessing the RAM is much faster than the speed of accessing the hard drive, which is why it is better if the data needed by the processor is already loaded into RAM.

The webs RAM

The RAM is in the form of webs which engage in slots provided on the motherboard. Thus the RAM is right next to the processor, and the bit circulation time is low …

The first PCs had very little RAM and it was made up of integrated circuits called ”  RAM chips. “. The “RAM chips” had a storage capacity of 16KB, 64KB, 256KB, or 1MB. For example, a 256KB x 1 (bit-wide) chip can store 256,000 bits, but it does. Eight was needed to store 256,000 eight-bit characters. The “RAM chips” were more or less fast, the time required to receive and store data is expressed in nanoseconds (a trillionth of a second), and the speed of the chips were 80, 120 or 150 nanoseconds. The “RAM chips” were called “bit-wide” (x 1), that is to say that eight “RAM chips” were needed to store a byte, each chip kept one of the eight bits of the byte. Each block of memory was made up of a set of “RAM chips”, at least eight for one byte and sometimes nine for parity. A block of memory was identified as a module. There were theSIMMs (Single Inline Memory Modules) and SIPP (Single Inline Pin Package) modules . The “RAM chips” or the modules could be located directly on the motherboard or on a ”  memory card  ” installed on one of the slots of the motherboard.

RAM technology has evolved over time and the connectors on the motherboard have adapted to new RAM modules. RAMs are less and less expensive, with an increasingly large storage capacity and an increasingly fast transmission speed.

The different RAM standards are not always compatible.

Standards PS / 2 72-pin and DIMM168-pin Dual Inline Memory Modules do not have the same number of pins and therefore cannot be mounted on the same connectors. Now all motherboards are equipped with DIMMs with an access speed of 10 NANOSECONDS. All the RAM modules on a motherboard must have the same access speed, otherwise, the slower speed is essential …

RAM modules that control the parity of the bytes recorded in a memory cells have an odd number of chips and a ninth bit that counts the number of ONE versus the number of ZERO. The new control mode which succeeds the PARITY mode, and which now equips DIMMs is called ECC (Error Correction Code).

New motherboards equipped with DIMMs are generally equipped with four connectors, the modules of which are no longer necessarily the same size, nor in even number.

Before changing the RAM modules, it is necessary to disconnect the power supply and discharge the static electricity of the human body by touching metal.

Procedures for Windows 98

To find out the amount of RAM installed on the computer (with the EXPLORER)

Open the

RIGHT-CLICK EXPLORER on THE

PROPERTIES WORKSTATION

PERFORMANCES tab

To find out the amount of RAM installed on the computer (with the “system” module)

START / DOUBLE-CLICK

CONFIGURATION PANEL PARAMETERS

on the SYSTEM module

PERFORMANCES tab

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