Nic Shulver, Fundamentals of Computer Networks Memory and Disc Drive hardware Working Memory and Permanent Storage

Nic Shulver, Fundamentals of Computer Networks Memory: RAM “Random Access Memory” isn’t random at all, it’s just not serial memory RAM is the rapid, working, temporary memory of the computer (n.b. don’t confuse with HDD or Flash)

Nic Shulver, Fundamentals of Computer Networks Memory: RAM Some RAM types: Low-power SDRAM Double data-rate RAM (DDR RAM) DDR2, DDR3, DDR4 (2013?) You need a specific type for a particular system A 32GB DDR3 RAM module

Nic Shulver, Fundamentals of Computer Networks RAM packaging RAM comes in many formats, including;formats 30 / 72 -pin SIMM – Very old! 168-pin DIMM 184-pin DDR 240-pin DDR2, DDR3 284-pin DDR4 (2013) DIL (classic chip shape) Flat, square high-density chips Speed information may be visible on the packaging

Nic Shulver, Fundamentals of Computer Networks RAM Performance RAM is usually sold based on the “Peak transfer rate” in megabytes per second DDR – DDR2 – 3200 to 8533 DDR3 – 6400 to DDR4 – double the data rate of DDR3 Faster RAM is more expensive, as you might expect (but obsolete RAM can be expensive, too)

Nic Shulver, Fundamentals of Computer Networks Latency Latency is the time taken from asking for the contents of a memory location to actually getting the answer Several measures tCAS – to access a column tRAD – to access a row tRP – to move from one row to another tRAS – overall value Expressed as a four figure number eg. Typical DDR2 – DDR3 – DDR – DDR –

Nic Shulver, Fundamentals of Computer Networks Cache It is possible to buy RAM to run at any given CPU speed (2 to 4GHz) But cheap mass-market bulk-storage RAM runs at around 200 to 800MHz (actual clock speed) Typical systems use cache memory built into the CPU as a buffer between the CPU and the “slow” RAM Cache can be 512KB to 8MB+ of very fast RAM This is a bit like a shop having items on the shelves rather than in the warehouse...

Nic Shulver, Fundamentals of Computer Networks CMOS RAM The CMOS RAM is special memory (sometimes a separate chip) that needs very little power to hold data Key system settings are kept in CMOS, e.g. hard- drive settings and various motherboard settings Most older PCs have 256 bytes of CMOS RAM Motherboards often have a “jumper” connection to clear it – useful when completely reconfiguring a system

Nic Shulver, Fundamentals of Computer Networks ROM Read Only Memory can be read but not written to The computer needs some instructions when it starts up - these are in the BIOS ROM Modern BIOS ROMs are so-called “flash ROM” Flash ROMs are a form of EEPROM [firmware] They allow BIOS updates without the need for physically swapping the ROMs But there can be safety & security problems!

Nic Shulver, Fundamentals of Computer Networks 10 Disc Drive types Serial ATA drives started taking over in 2003 (start at 150MBps, now does 300MBps [2006], 600MBps [2008] ) SCSI is the Small Computer Systems Interface, a smart, fast but more expensive system commonly found in PC servers and older Macintosh systems (up to 80MBps) SCSI has all but vanished at the low and mid-price points – only has a place with very fast drives

Nic Shulver, Fundamentals of Computer Networks 11 IDE/ATA and SATA

Nic Shulver, Fundamentals of Computer Networks 12 HDD - Hard Disc Drives Change has been rapid over the last twenty years “Fast mass-storage” once meant 80ms access time for 10MB hard drives, now 8ms access time and over 1000GB (one terabyte) is common Matchbox-sized drives for cameras and media players can have over 500GB of storage room

Nic Shulver, Fundamentals of Computer Networks 13 External Storage Most external storage devices do not required manual installation. Uses: Expanding storage on notebook or PC Transporting large amounts of data Backing up Offline data storage

Nic Shulver, Fundamentals of Computer Networks External Hard Disk 3 different types of interface USB FireWire External SATA 3 different sizes Full size – PC Hard disk size, 3.5 inches width Portable size – Laptop hard disk size, 2.5 inches width Pocket size (not popular as they have small capacity which can be replaced by Flash memory)

Nic Shulver, Fundamentals of Computer Networks Flash Memory USB flash memory 1MB/s (USB 1.1) or up to 60MB/s (USB 2.0) Typically 1GB to 64GB of storage U3 Smart USB Drive Micro SD and Mini SD (HC) Use in mobile phones, digital cameras, PDAs Up to 64GB of storage SD and SDHC Use in PDAs, cameras – was popular Up to 1GB of storage for SD 64GB+ for SDHC

Nic Shulver, Fundamentals of Computer Networks Solid State Drives According to Seagate, 2010 total market for notebook HD storage was 69 exabytes (69 billion gigabytes) ( forecast - a rise to 95 exabytes (Gartner) In 2010 the total NAND memory manufactured was 11 exabytes, only 7% found its way into SSDs It would take $250 billion investment in new fabrication plants to meet demand in SSDs are not going to take over yet!

Nic Shulver, Fundamentals of Computer Networks Summary We have discussed the basic of different types of storage that are used in the PCs Memory Performance Speed or Bandwidth of memory Cache CMOS RAM ROM Disc Drives Flash Drives, SSDs

Nic Shulver, Fundamentals of Computer Networks References, Reading DDR Memories Comparison and Overview DDR4 SDRAMFrom Wikipedia CPU cache From Wikipedia