nic shulver, [email protected] fundamentals of computer networks memory and disc drive...
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Nic Shulver, [email protected]
Fundamentals of Computer Networks
Memory and Disc Drive hardware
Working Memory and Permanent Storage
Nic Shulver, [email protected]
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, [email protected]
Fundamentals of Computer Networks
Memory: RAM
Some RAM types:Low-power SDRAMDouble data-rate
RAM (DDR RAM)DDR2, DDR3, DDR4
(2013?)
You need a specific type for a particular system
http://www.samsunghub.com/wp-content/uploads/2009/06/32GB-DDR3-RDIMM.jpg
A 32GB DDR3 RAM module
Nic Shulver, [email protected]
Fundamentals of Computer Networks
RAM packaging
RAM comes in many formats, including;30 / 72 -pin SIMM – Very old!168-pin DIMM184-pin DDR240-pin DDR2, DDR3284-pin DDR4 (2013)DIL (classic chip shape)Flat, square high-density chips
Speed information may bevisible on the packaging
Nic Shulver, [email protected]
Fundamentals of Computer Networks
RAM PerformanceRAM is usually sold based on the “Peak transfer
rate” in megabytes per secondDDR – 1600 - 3200DDR2 – 3200 to 8533DDR3 – 6400 to 17066DDR4 – double the data rate of DDR3Faster RAM is more expensive, as you might
expect (but obsolete RAM can be expensive, too)
Nic Shulver, [email protected]
Fundamentals of Computer Networks
LatencyLatency is the time taken from asking for the contents of a
memory location to actually getting the answerSeveral measures
tCAS – to access a columntRAD – to access a rowtRP – to move from one row to anothertRAS – overall value
Expressed as a four figure number eg.Typical DDR2 – 5-5-5-15DDR3 – DDR3-1066 – 7-7-7-21 DDR3-1333 – 7-7-7-24
Nic Shulver, [email protected]
Fundamentals of Computer Networks
CacheIt 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, [email protected]
Fundamentals of Computer Networks
CMOS RAMThe 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 RAMMotherboards often have a “jumper” connection to
clear it – useful when completely reconfiguring a system
Nic Shulver, [email protected]
Fundamentals of Computer Networks
ROMRead Only Memory can be read but not written toThe computer needs some instructions when it
starts up - these are in the BIOS ROMModern 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 ROMsBut there can be safety & security problems!
Nic Shulver, [email protected]
Fundamentals of Computer Networks
10
Disc Drive typesSerial 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, [email protected]
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, [email protected]
Fundamentals of Computer Networks
13
External StorageMost external storage devices do not required
manual installation.Uses:
Expanding storage on notebook or PCTransporting large amounts of dataBacking upOffline data storage
Nic Shulver, [email protected]
Fundamentals of Computer Networks
External Hard Disk3 different types of interface
USBFireWireExternal SATA
3 different sizesFull size – PC Hard disk size, 3.5 inches widthPortable size – Laptop hard disk size, 2.5 inches widthPocket size (not popular as they have small capacity
which can be replaced by Flash memory)
Nic Shulver, [email protected]
Fundamentals of Computer Networks
Flash MemoryUSB flash memory
1MB/s (USB 1.1) or up to 60MB/s (USB 2.0) Typically 1GB to 64GB of storageU3 Smart USB Drive
Micro SD and Mini SD (HC)Use in mobile phones, digital cameras, PDAsUp to 64GB of storage
SD and SDHCUse in PDAs, cameras – was popularUp to 1GB of storage for SD64GB+ for SDHC
Nic Shulver, [email protected]
Fundamentals of Computer Networks
Solid State DrivesAccording to Seagate, 2010 total market for
notebook HD storage was 69 exabytes (69 billion gigabytes) (http://www.pcworld.com/businesscenter/article/217883/seagate_solidstate_disks_are_doomed_at_least_for_now.html)
2011 forecast - a rise to 95 exabytes (Gartner)In 2010 the total NAND memory manufactured
was 11 exabytes, only 7% found its way into SSDsIt would take $250 billion investment in new
fabrication plants to meet demand in 2011...SSDs are not going to take over yet!
Nic Shulver, [email protected]
Fundamentals of Computer Networks
SummaryWe have discussed the basic of different types of
storage that are used in the PCsMemory PerformanceSpeed or Bandwidth of memoryCacheCMOS RAMROMDisc DrivesFlash Drives, SSDs
Nic Shulver, [email protected]
Fundamentals of Computer Networks
References, Reading
DDR Memories Comparison and Overview
DDR4 SDRAMFrom Wikipedia
CPU cache From Wikipedia