Dynamic storage units

Rudometov E, Rudometov Century
authors@rudometov.com

Miniature SIMM-units, or it is simple SIMM, represent blocks of dynamic storage of different size. The wide circulation was found SIMM on 4, 8, 16, 32 and even by 64 Mb.

SIMM happen two different types: on 30 pin and 72 pin where pin ("pin") means number of contact electrodes of hooking up to the specialised plug of the working memory on the motherboard. Thus 30 pin and 72 pin SIMM — not interchangeable units.

SIMM differ in the speed of operation. Usually in the PC on processors 486 arrangements on 70 nanoseconds though for type processors 486DX4–100, 486DX4–120, 486DX4–133, Pentium, it is recommended to use SIMM at least on 60 nanoseconds were applied  .

There is no necessity to prove, that high-speed parametres of memory modules are one of the main characteristics, however their dependability and stability to possible glitches are not less important. To rise of the given metrics for units by improvement of processing technique of their production and perfection of the architecture of computers the most steadfast attention is paid. One of the solutions raising dependability and noninterference of functioning of a subsystem of memory, introduction of special circuits of the control and redundant coding of the information is.

Memory modules happen to parity check (parity) and without parity check (non parity). The given function allows to inspect working memory operation, interrupting the program at memory glitches. Units with parity check it is more difficult, and their price a little above. In many cases application of such units is justified. However, considering high dependability of modern circuitry of computers and used units, in particular the working memory chips, many manufacturers of a computer technology are oriented to usage of units without parity check. Corporations-manufacturers consider this function inexpedient for single computers and for workstations in a network.

Rise of dependability of chips of memory can be observed on a following example. At creation in recent times for already out-of-date models of computers of 1 Mb of the working memory from chips on 16 Kbit one glitch of memory was observed at the best through 100–150 business hours. Certainly, at such dependability of bats of accuracy it is necessary. For the last years dependability of chips of memory has increased in some thousand times, and for the working memory in 4 Mb (8 chips on 4 Mbit) one glitch of memory should be observed on the average for the period approximately in 10 years of continuous operation, for 16 Mb — 4 SIMM on 4 Mb — 2–3 years etc . By the way, all it is true not only for SIMM, but also for units of more modern design (form factor).

Dependability and failure rate of RAM chips depend on complexity of used chips: the above the degree of their integration and, accordingly, information capacity of chips of memory applied as a part of units, the better processing technique, is less than chips, dependability of memory and more low the value of failure rate is less than interconnections, above. It means, that the non-failure operation period, for example, for the units generated on the basis of memory cells on 16 Mbit, more than for units on the basis of units on 4 Mbit. Thus, it is better 1 SIMM on 16 Mb, than 4 SIMM on 4 Mb.

Certainly, higher dependability is characteristic for the units concerning to category of arrangements and units brand name, and it is essential more low — for no name units.

Estimating offered memory modules with parity check, it is necessary to know, that in the market of accessories there are various variants of similar products. For some a parity bit and control bit are substituted by the special circuit of emulation of these functions. In this case, of course, no real control is present, and such units do not raise operational reliability of the PC. However similar products essentially more cheaply also can represent defensible interest for those users from whom motherboards for the correct operation demand parity bit presence.

Memory with parity check as it was already marked, allows to instal the fact of glitch of the working memory only. The analysis and appropriate solution is fulfilled by a computer firmware. In the same cases when it is necessary to restore the information without operating procedure violation, expediently to use dynamic storage with an error correction — ECC-memory. The given function is reached by redundant hardware coding of data in the working memory and usage of various codes of selfrecovery of the information. Certainly, such memory modules are much more expensive than usual, not providing data of functions.

The wide circulation was found by RAM chips EDO DRAM (Extended Data Output — memory with the expanded output). Such memory is a little bit more expensive before developed chips FPM DRAM (Fast Page DRAM), but allows to increase high-speed performance of a subsystem of memory, and, therefore, and the common computer power. As a rule, this gain makes 3–5 %.

Before to use SIMM EDO, it is necessary to be convinced that the motherboard supports normal operation of this type of memory. Usually these types of memory well work in computers with Pentium processors, but is rather rare in the systems grounded on processors 486.

At a choice and acquisition of memory for the PC it is necessary to consider, that some SIMM, oriented to usage in certain computers, usually in the PC brand name, can be incompatible for the architecture of other PCs. Examples when SIMM not all memory sizes can be used with the concrete motherboard are besides, known. For example, for some motherboards do not approach SIMM in size of 8 Mb.

For an exception of the errors linked to acquisition and usage of improper memory modules, it is expedient to access in the presence of due qualification to the appropriate technical literature or at a lack of experience and knowledge to search the help for experts-professionals.

Memory modules, as well as other units of computers, are permanently perfected. Regularly there are new types. Everyone some years occur change konstruktiva units. The bus extension through which dynamic storage hooking up is carried out, has demanded depositing of respective alterations for units. Have appeared DIMM (Dual In-line Memory Module). Computers on the basis of Pentium processors, Pentium Pro, Pentium II have the data bus of 64 bits. The necessary number of memory modules for bus occupancy is named as a memory bank. In case of a 64-bit wire for this purpose it is required two 32-bit 72-contact SIMM units or one 64-bit DIMM unit having 168 contact electrodes.

3,3 V.Nebuferizovannyj DIMM unit are standard nebuferizovannye (unbuffered) units with a supply voltage can contain chips of memory of type FPM DRAM, EDO DRAM, BEDO DRAM, SDRAM. Units can have 64 bits or 72 bits (parity check), and also 72 bits and 80 bits for ECC. The construction of units provides their automatic recognition by the computer. Special keys — notches in the contact bar for this purpose use . Left — buferizovannyj or nebuferizovannyj, right — a supply voltage — 5 In or 3,3 Century

Constant growth of productivity of processors and perfection of electron technologies stimulate engineering processes of new types of dynamic storage. Appearance of memory Direct Rambus DRAM — Direct RDRAM has demanded new konstruktiva for memory modules. Chips Direct RDRAM are gathered in RIMM units outwardly similar standard DIMM, that, by the way, and has found reflexion in the name of units new konstruktiva.

On RIMM unit card can be to 16 chips of memory Direct RDRAM installed on eight pieces from each side of the card. RIMM units can be used on motherboards with standard form factors, for example, such as ATX. Thus usage of RIMM units probably only as a part of systems, BIOS and which chip sets are calculated for usage of the given type of memory. For example, in case of specialised sets of the corporation of Intel it there can be such chip sets as i820, i840 and their modifications. According to guidelines of usage of RIMM units in the motherboard architecture can be to three plugs under the given units.

From features of maintenance of RIMM units it is necessary to mark, that units of this type demand intensive cooling. It is linked with considerable them energopotrebleniem and accordingly a heat release that is caused by high high-speed performance of the given memory modules. Nevertheless, manufacturers of RIMM units consider, that a problem of a high heat release it is possible to decide the accelerated implantation of a new procedure of production of chips of memory Direct Rambus DRAM, for example, 0,13–0,1 microns that is accessible within the next 2–3 years. Practically all main manufacturers of chips and memory modules have declared support of processing technique Direct Rambus and have adjusted their production.

Though outwardly RIMM units remind DIMM units, however they have smaller number of contact electrodes and from both sides are closed by the special metal screens, not used in the previous memory modules. The given metal screens protect RIMM units working on the big frequencies, shielding their sensitive electronic circuits from external electromagnetic navodok. Screens Besides, used in construction RIMM reduce mutual influences of adjacent memory modules.

Now the accepted specifications supported, by the way, by the corporation of Intel, define three types of the units, differing operating frequencies and capacity. They are designated as RIMM PC800, RIMM PC700, RIMM PC600. The Most high-speed are RIMM PC800 units with clock rate of 400 MHz and capacity of 1,6 Gbytes/with. RIMM PC800 units and RIMM PC700 are intended for operation on the raised frequencies of the bus of memory, for example, on the frequency of 133 MHz supported by modern chip sets.