[NTLK] Why a Newton Never Forgets

[Andrei Chichak]

Hi Thomas,

I'm not sure what part of the myapplenewton blog you don't understand, so let me give it another try.

A lot of people have no idea how computers work and one of the biggest points of misunderstanding is the two types of memory utilized in computers. We have all been asked "how many rams does your computer have?", an odd question and one that indicates that the person asking the question really doesn't understand what they are asking. 

RAM is an acronym meaning "Random Access Memory". All that this means is that any element of the memory can be accessed without going through all of the preceding information. So, what is the opposite of RAM? ROM, no, it is tape. A tape has to be read from beginning to get to the information that you need. This is sequential access memory.

ROM is an acronym meaning "Read Only Memory". This is memory that you can only read, it cannot be written. 

Back in the bad old days we had chip memory that was ROM, it was prepared at the factory and could not be updated "in the field". These chips could be purchased, empty, and programmed by geeks. These were known as PROM (Programmable Read Only Memory). On the older Macs, most of the operating system routines were in ROM.

Later EPROM was invented (Erasable Programmable Read Only Memory). This is a ROM that can be erased and reprogrammed, but you needed a high intensity UV light source to erase them and special programmers to program them. These were chips with a little window on the top so the UV could penetrate. They typically have a sticker over the window and were heavily used for the boot ROMs (bootstrap read only memory) on computers. The old PROM was now known as OTPROM (One Time Programmable Read Only Memory).

Later again, the electrical engineers figured out how to erase these chips without the UV light and program them while they were installed in a circuit without any special equipment. This was originally known as EEPROM (Electrically Erasable Programmable Read Only Memory), and later FLASH (which isn't an acronym, they were just yelling). The big difference between EEPROM and FLASH is that EEPROM will erase a single byte whereas FLASH erases a "page" or about 512 bytes. FLASH uses less transistors per byte, so you can put down more in a chip but you have a larger erase granularity.

With all of the ROM types, the computer doesn't write new data into the chips in normal use. Good thing, since these chips can only be erased and reprogrammed between 100 and 1,000,000 times before they either don't program properly, or they may start to forget.



Another form of memory, now known as RAM, is the high speed main memory. There are two forms, dynamic and static (DRAM and SRAM). DRAM will forget its values unless the processor refreshes (basically continually updating) it very frequently. It is like a leaky bucket. SRAM will only forget its values if you remove all power sources from it. SRAM is small capacity, expensive, but very fast. DRAM uses less transistors and can have a larger capacity, less expensive, but not quite so fast.

PROM, EPROM, EEPROM, and FLASH does not forget its contents when power is turned off.

 Disks, floppy disks, and tape do not forget their contents when the power is turned off, they can be huge (compared to main memory), but they are slow, and cheap.

Certain alterations to the language were made due to familiarity, main memory is now called RAM, generically, the chips where the system startup code is kept is called ROM, even though it is typically FLASH, and those new solid state disks are disks even though they are made up of FLASH.


A while back I went to a Microsoft Windows CE developer's conference where I was given a Casio PDA. It used SRAM for all of its memory. Once the batteries died it forgot everything, all of my notes, all of my calendar events, everything. No respect for my data.

Fanboyz will now chime in and start stating megs and part numbers but... The Newton, by design, used SRAM for calculations, it would hang around until the batteries died. Apple used a backup battery to hold the SRAM values while you replaced the main battery. If both died, it would forget. 

Later, Apple incorporated FLASH memory to store your data. As changes to the soup happen, they are compressed and written through to a big chunk of FLASH. FLASH is designed not to forget. So if you have data on your Newton and the batteries go dead, and you put it in a drawer for a few years, the data is still there waiting for you to come back.

A


On 2011-January-29, at 4:40 PM, Thomas Brand wrote:

> Long time, no post. For a new Egg Freckle I am writing (eggfreckles.net), I am looking for a detailed explanation on why a "Newton Never Forgets" its data. I have read this detailed blog post on My Apple Newton about MessagePad memory (http://myapplenewton.blogspot.com/2009/04/newton-memory-101.html), but a encompassing conclusion that answers my question evades me. Any good resources out there?
> 
> Thanks,
> Thomas Brand
> 
> 
> 
> 
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