PC Repair II Notes and Lab on Memory  

I.                   Types of Memory

Your system has RAM, and Cache memory on the motherboard and CPU.   RAM is stored on the motherboard.  L1 and L2 are cache memory, stored on the the Motherboard or on the Processor.  Cache memory is much faster, but more expensive than normal RAM.  Adding cache memory speeds up the PC, but makes it more expensive. Some processors are limited in RAM by the amount of RAM that can be cached.  For example if your processor can only cache 128 Megs of RAM, expanding to 256 Megs may actually slow down your PC!  Make sure you know if your PC can cache the extra RAM you want to add before even considering adding it!  Most current processors have 128K to 512K cache, the more the better!

II. Memory Handling in Win 9X

Win 9X accesses the protected mode of the x86 processors and as such can access much more than the 1 Meg allowed in DOS.  This memory is divided into parts in Windows.  Windows can also page or swap memory from RAM to the Hard Drive to make it appear to have even more memory than the actual RAM.  Since the Hard Drive is much slower than RAM, when this occurs there is degradation in speed.  This memory is called the SWAP File.

System Memory is the total memory available to Windows: base, extended, virtual (swap file).

Virtual memory is "fake memory," where a portion of the hard disk is used as overflow memory.

Windows 95 creates a temporary swap file (WIN386.SWP) that changes according to need.  This is an option that can be overturned.  You can allocate a fixed size and location of swap memory for windows.

To adjust the Windows 95 swap file, double-click the System icon in the Control Panel and select the Performance tab followed by Virtual Memory.

Although it is lesser known, GDI Heap is memory that is used to store the graphical elements of Windows, such as icons and bitmapped images. If you run programs that use many bitmaps, icons, and so on, you might run out of GDI Heap.

The User Heap is memory that is used to hold information about active windows and other related information. In Windows 3.x, the Menu and String Heaps are included in the User Heap. This heap is also only 64K.

You can also obtain DOS memory information from within Windows 95.

30 PIN vs 72 Pin Vs 168 PIN

Sips (Single Inline Pins), SIMMS (Single Inline Memory Module), DIMMS (Dual Inline Memory Module 168 PIN, 64 BIT, normally SDRAM now).

Installing/Replacing Memory

Newer computers rely on DIMMS while older machines rely on SIMMs and sometimes SIPs for extra memory. If you have a vacant memory bank, you can install this type of extra memory. SIMM, DIMM, and SIP memory are similar; several memory chips are bundled into one package. Unlike DIP memory, SIMM/DIMM/SIP memory enables you to install the equivalent of nine chips in one motion, rather than one at a time.

First you need to get the right memory.  For this you need to look in the book which came with the computer and find out what type, and speed and capacity your PC will take.  Then purchase the memory from a computer parts store, the internet, or a place like Office Depot.  Make sure you have the empty space to put the chips, or you may need to take out the existing chips and replace them with larger capacity ones!

1.                  Turn on your PC, make sure everything is working correctly, and record the current amount of memory.  _______________ (you can tell this in windows 9X by right clicking my computer and left clicking properties).  If you have diagnostic software see if you can tell how much Cache Memory is present.

2.                  Shut down windows and if necessary turn off  the computer and remove its case.

3.                  Ground yourself by touching the case on direct metal, then uplug the PC.

4.                  Locate the banks of memory chips and the vacant memory bank.

5.                  You usually see two memory banks that hold four SIMMs or SIPs each. Pentium computers use two banks of two SIMMs. The newer 168-pin DIMM style of memory has up to 4 banks of one DIMM each. DIMM banks can be in addition to two 72-pin SIMM banks.

6.                  Jot down the numbers on the SIMM/DIMM/SIP memory chips in the full memory bank and order additional memory for the vacant bank.The chips in the other memory bank are probably the type of memory chips you need to order. The current SIMM/SIP chips probably have these numbers within the chip's part number, which is printed on the top of the chip.

SIMM/DIMM/SIP Type            Size

1256    256K x 1 bit
14256  256K x 4 bits
11000  1024K x 1 bit
14400  1024K x 4 bits
41000  4096K x 1 bit
44000  4096K x 4 bits
For example, one of my older computers has 8M of memory, or four 1M SIMMs in each bank. The first bank has SIMMs made of three chips each. Two of the chips are of the 14400 kind (1024K x 4 bits), which together make up eight bits. The third chip, the ninth bit, is an 11000 chip (1024K x 1 bit) that checks the accuracy of the other two. The second memory bank uses SIMMs composed of the typical nine chips, one for each bit. It doesn't matter what type of chip is used for the SIMM/SIP, although a three-chip SIMM/SIP requires less room. In my computer, the three-chip SIMMs are shorter, enabling me to install an expansion card over them.

If you have a vacant memory bank, you probably want to add chips that match the current ones. For accuracy, consult the owner's manual about the type of chips to add. If you don't have an owner's manual, consult the previous table of possible memory configurations for SIMM/SIP chips. Remember that if you add extra memory to the computer, its speed must be equal to or less than that of the memory that is already installed.

7.                  Install the SIMM/DIMM/SIP memory into the sockets.

8.                  Each SIMM/DIMM/SIP must be installed pointing in a certain direction. Each chip has a polarity notch on one end of the circuit board. A SIMM has a notch cut into one side and mounting holes into which metal clips fasten. A SIP has a diagonal notch. A DIMM, meanwhile, relies on two notched keys in the socket that prevent it from being installed incorrectly. If the module is reluctant to enter its socket, try turning it around.

9.                  Place each SIMM/SIP at about a 45-degree angle, lining up the copper-colored connectors on the memory module with the socket on the motherboard. The chips on the module face away from the angle of the socket. Because four modules must be installed into the bank, you must insert the modules in a certain order so that each subsequent module has room to be inserted at this angle.

10.              Firmly insert the SIMM into the socket. Next, pivot the SIMM backward to an upright position until it touches the plastic latches on both sides of the socket. Carefully press the SIMM against these latches until they snap around the edges of the SIMM, and then clamp it firmly into place. The circuit board that serves as the backbone of the SIMM needs to be perpendicular to the circuit board that holds the socket.

11.              A plastic or metal finger from the socket latch should poke slightly through the alignment hole at the edge of the SIMM (if the SIMM has holes), or the side latches of the socket should wrap around the board of the SIMM. For each SIP, insert the module straight into the SIP socket. You should feel the SIP slide into the grasp of the socket's contact fingers.

12.              For 168-pin DIMMs, insert the module straight down into the socket until the clips hold it in place.

13.              Replace the case, and restart the PC

14.              Make sure the BIOS recognizes the new memory. It may be necessary to save the BIOS with the new settings, if you have changed the amount of memory in the PC.

15.              Start the OS and determine how much memory you have now.________________
Instructor ok ____________________