Re: cron oddity?
(someone wrote, regarding different ls output) sudo ls -lGgh /srv/ftp/pub -r--r--r-- 1 14M Nov 7 16:02 GE_Mainline_Ansys ver2.ppt HUH? when I do it manually the output is sudo ls -lGgh /srv/ftp/pub -r--r--r-- 1 14M 2006-11-07 16:02 GE_Mainline_Ansys ver2.ppt As others have said, it might be an environment variable. It is also possible that there are different versions of ls in different directories, such as /bin/ls, /usr/bin/ls, or even /sbin/ls or /usr/sbin/ls. Changes to the path would then change which one was used. I have run into this more often with ps, where a ucb-like ps and SysV like ps exist on the same system. -- glen
360/30 timing
Jim Bohnsack wrote: Back around 1970 or so, I did a performance study on a S/360-30. At that time, IBM published instruction times somewhere--don't remember where. But I came up with a result that said that a mod 30 was an 18 kip machine. For some reason I have the 360/30 Functional Characteristics sitting next to my computer, instead of upstairs where it is supposed to be. AR22us ADR 61us CP45+4M us DR413us DDR 1619us MVC 31+3N us SRDA 76us SVC 44us 18 kips would be 56us, maybe about right assuming not too much floating point. -- glen
TCP ports and SMTP clients
Alan Ackerman [EMAIL PROTECTED] wrote: Usually, high port numbers are assigned to clients. Clients on VM include FTP, TELNET, NFS, and Charlotte (web browser). That is usual for most TCP/IP systems. High source ports are assigned to any client, not just the obvious ones. All the more reason why they MUST get you the contents of (some of) the packets. With that you might be able to identify which client. Why did they think it was email, if they could not see the contents of the packets? As designed, TCP and UDP ports under 1024 are reserved, and on most systems non-privileged users can't use them. Other than that, there is usually no restriction on which port numbers can be used by client or server. Note, though, that it is easy to connect to any destination port, with no privilege normally required. On unix systems, mail is usually sent directly by sendmail run by the sender. Anyone can open a connection to port 25 and type SMTP commands into that connection. That is TCP/IP as designed. -- glen
3270 data stream
I have scanned GC23-0059-2, 3270 Data Stream Programmers Reference, and sent it to bitsavers. I don't know that it is actually available yet. I do see that Gc23-0059-7 is available from IBM in paper or electronic form. -- glen
Re: block letter routine
The source to older versions of JES2 and JES3 are available, at least I believe they are. It must be in there somewhere. -- glen
Cleaning Fluid
David Boyes [EMAIL PROTECTED] wrote: Does anyone still know of a source that sells 3420 cleaning fluid and supplies? In the process of working through these old tapes from Princeton, I'm burning through the small supply I have of the stuff rapidly (2 pints so far), and still have a few thousand tapes to go.=20 The popular cleaning fluids are mixtures of isopropanol and 1,1,2 Dichloro 1,2,2, Difluoro ethane, I believe called Freon TF. I have no idea if that is what yours is, though. Ordinary rubbing alcohol is 70% isopropanol, but many stores (grocery stores or drug stores) also have 99% isopropanol. If you have a near by chemistry lab you can get reagent grade, which is probably 99.99% or so. (Not counting the water that will get in as soon as you open the bottle.) The amount of oxide flaking and just general destruction these tapes have is amazing - gunk everywhere. Hats off to the data recovery folks - I'd really hate to have to do this all the time. Freeze drying, careful rereading, multiple retries... sheesh. Phase of the moon for some of these volumes.=20 Are you warming the heads? I have heard over the years that it the favorite way to reduce flaking. The first time I heard that one was an article in Popular Science about a video tape recorder that used 0.25in tape linear recording at 120in/s. (Many years before Beta, or even U-matic.) Warming the heads was necessary to prevent scraping the oxide off even of new tapes at that speed. There is also supposed to be a last chance system that uses a fluid, such as cleaning fluid, on the head while reading the tape. As I understand it, it only works once. After that, the tape is ruined. I have never tried, or even seen this done, though. -- glen
Token Ring vs. Ethernet
Rich Seifert (who worked on the original 10Mbit ethernet) in his Gigabit Ethernet book has some explanation about this. Token Ring requires more complicated hardware, keeping the price higher. The higher price reduces demand, making it harder to reach the economy of scale point. There is a lot of hardware to manage tokens, create one if the active token is lost, etc. Also, TR has a priority system allowing eight priority levels. There is no system to manage or assign priority, so everyone uses the highest priority level, making the extra hardware useless. There is a story about a conference where IBM announced the TR card for the original IBM PC. Someone asked about ethernet, and the speaker suggested that if one found an ethernet card for less than $200, buy it. The next speaker was from 3com announcing the 3C501 for $199. (I believe I have the prices right, but it has been some time since I first heard this.) -- glen
Dumb IP Question
Tom Duerbusch [EMAIL PROTECTED] wrote:
From my understanding, when a client connected to the server stack at a
particular port, that port is tied up and no one else can connect to
it.
If I remember correctly, when you FTP to port 21, the FTP server
responses with another port that you should use for the rest of the FTP
session. This keeps port 21 from being tied up during long FTP
sessions. Right?
As far as TCP is concerned, a connection is identified by the
{source address, source port, destination address, destination port}
combination. When a packet comes in, that is what is used to find
the appropriate destination. Since TCP is a stream protocol,
the packets are processed by TCP, retransmissions are requested,
and data is delivered only after it is back in stream format.
Boundaries between requests to TCP don't necessarily generate
separate TCP packets, and packet boundaries aren't seen on
by receiving program.
UDP usually only processes the {destination address, destination port}
combination. Some servers will decode the source address, source
port, but it is the responsibility of the receiving program.
Many stateless servers can handle UDP without a subtask for
each client, just replying to each request. Data is delivered
preserving packet boundaries.
Under unix, programs accepting a TCP connection usually fork()
to create a subtask to handle the connection. It might be that
new requests that come in before the fork() get the busy signal.
Most print servers boxes can only handle one connection at a time,
and will refuse any additional connections. That is not a TCP
limitation, but a higher level protocol limitation. Sendmail,
I believe, also refuses connections when too many are already
open to avoid overloading the machine.
-- glen
Virtual memory implementation in S/370
(I wrote) VAX uses a two level system where page tables are paged. There is kernel space, which isn't paged and holds the first level tables referencing pagable second level tables. z/Archtecture has three levels. (someone else wrote) Actually, z/Architecture has 5 levels. So far, the existed hardware only uses 3 of them. I thought of that right after sending it. Above the addressing within a page, it is, more or less, 10 bits per level. (For S/370, one could consider the 32 bit addressing for the 360/67, which is fairly similar.) For an undergrad operating system course I did a report comparing S/370 and VAX virtual memory systems (around the time when VAX was new). I remember finding more similarities than differences, especially both using the two level system. So for 64 bit addressing of 4K pages, (64-12)/10 is about five. Allowing the hardware to use three until more addressing bits are needed is a nice feature. -- glen
Virtual memory implementation in S/370 (a.f.c x-post)
Marten Kemp [EMAIL PROTECTED] writes: The recent thread about virtual memory sparked a (kind of) idle question: why did the implementation in the S/370 have a two-level scheme (segment and page)? My original thought was that it facilitated definition of discontiguous parts of an address space. Well, mostly it is because smaller systems don't have enough real memory to hold a one level page table. The segment/page system allows page tables to be paged out, with the invalid bit in the segment table. VAX uses a two level system where page tables are paged. There is kernel space, which isn't paged and holds the first level tables referencing pagable second level tables. z/Archtecture has three levels. -- glen
